I got a brand new bellows a few weeks ago and an issue arose in relation to the air inlet valve. The bellows was perfectly airtight, but I found that the inlet valve was a little too tight and efficient. This meant that the bellows wasn't drawing in air as quickly as I could on my old bellows. So I removed the valve and made it a little bit looser - first by reducing the width of the valve hinge and also by manipulating the valve itself so that in resting state it is hanging a little loose off the end of the inlet pipe.

What this does is allow me to draw in air with a lot less effort and also, which is important in playing terms, to draw smaller amounts of air without making a full sweep of the bellows, so less effort and motion of the bag arm is required to get the air supply that I need. It might seem that loosening the valve would reduce overall efficiency of the bellows, but actually it works out that the looser valve improves playability by making the bellows intake more responsive.

Yes - the new bellows are working fine. I think the key was to have the inlet flap hanging a little open in the resting position. In this way, little or no effort is required from the player's elbow to open the bellows on the outward sweep. Of course the flap closes immediately at the start of the inward sweep, so no loss of efficiency in terms of air delivery to the bag.

Mechanically speaking I think this inlet is defined as a non-return clacker valve - so it allows easy (does not resist) inward movement of air, but completely closes down any flow back out. It's a simple thing - but if this valve is too tight it can make the bellows operation much more strenuous than would be comfortable for playing.